1. Field of the Invention
The present invention relates to a pneumatic safety tire which is reinforced at side portions and enables satisfactory use under the run-flat condition.
2. Description of Related Art
As tires which are pneumatic and can be used under the run-flat condition (these tires are referred to as pneumatic safety tires) or tire wheels having the same property, tires of an internal wheel type in which an annular internal wheel made of a metal or a synthetic resin is attached to a rim in the pneumatic chamber of the tire and tires of a side reinforced type in which portions of side walls from bead parts to shoulder areas are reinforced by layers made of relatively hard rubber having a crescent-shaped cross-section disposed at an inner side of a carcass (Structure I in FIG. 2) have been known. Between tires of these two types, tires of the internal wheel type have been regarded as useful to some degree for vehicles for transportation of goods and military vehicles which are not particularly required to have a good riding quality. Tires of the side reinforced type have been regarded as useful to some degree for passenger cars which are loaded with a relatively light weight and are required to have a good riding quality its important property/quality.
In a tire of the side reinforced type, the tire is reinforced by a relatively hard reinforcing rubber layer having a crescent-shaped cross-section disposed at the inner side of the side wall in such a manner that an end portion of the reinforcing rubber layer overlaps belt layers, with the carcass being between the belt layers and the reinforcing layer, and another end portion overlaps a rubber filler. When the tire is punctured during use and pressurized air is lost, the weight is supported by the rigidity which is inherent to the side walls reinforced with the reinforcing rubber layer, and the vehicle can be driven in specified distance under the run-flat condition although the speed of the vehicle must be somewhat decreased.
As described above, various safety tires of the side reinforced type have heretofore been proposed. However, most of the proposed tires are used as ultra-low profile high performance tires, i.e., tires having a low aspect ratio and used for vehicles having a relatively small axle load, such as sports cars, but those tires do not show sufficient durability under the run-flat condition. The aspect ratio is expressed as {(height of a tire)/(width of a tire)}xc3x97100 under the condition that the tire is attached to a rim, and an ultra-low profile tire is a tire having an aspect ratio less than 60%, such as 30 to 40%.
However, as safety is required increasingly in recent years, safety tires are required also for general use tires for passenger cars which have an aspect ratio of 60% or more.
Although a load applied to a tire is relatively small in the case of a general use tire for passenger cars, the load per one tire may be as large as 500 kgf in the case of larger passenger cars. In such a case, deformation of side walls under the condition of puncture is increased, and the side walls are completely buckled under a dynamic load which is formed by driving and is several times as large as that under the normal condition. This buckling repeatedly takes place during driving. As the result, the bead part in the side wall is pushed up by a flange of the rim, and a covering rubber and a turned-up portion of the carcass which are squeezed between the curved flange and the rubber filler melt or fracture by heat. When this occurs, the tire cannot be used any more even after the part which caused the puncture has been repaired.
As the result of intensive studies comparing ultra-low profile high performance tires and general use tires for passenger cars, the following differences have been found.
a. Because general use tires for passenger cars have larger heights than those of ultra-low profile high performance tires, general use tires show larger deflection under load.
b. Because general use passenger cars generally have larger weights than those of sports cars to which ultra-low profile high performance tires are attached, general use passenger cars cause larger load to the tires.
Because of the characteristics a. and b. described above, the temperature within a tire is not very high when an ultra-low profile high performance safety tire is used under the run-flat condition. In contrast, the temperature within a tire reaches a temperature as high as or higher than 200xc2x0 C. when a general use size safety tire for passenger cars is used under the run-flat condition. Therefore, it must be considered that the temperature within a tire during use is different depending on the type of the tire.
On the other hand, a decrease in weight of a tire is strongly required in order to decrease the fuel consumption of a vehicle. To decrease weight of a tire, thickness of a side wall of the tire tends to be decreased more. It is required that use under the run-flat condition, i.e., at the internal pressure of the tire of 0 kg/cm2, must be possible, and at the same time, satisfactory properties during ordinary use under an inflated condition are naturally required.
The first object of the present invention is to provide a pneumatic safety tire having an aspect ratio less than 60% and, exhibiting a small deflection because of its small height and use thereof under a small applied weight, maintaining properties during ordinary use under an inflated condition at high levels, enabling decrease in the weight, and showing remarkably improved properties under the run-flat condition in comparison with those of conventional safety tires having a rubber reinforcing layer.
The second object of the present invention is to provide a pneumatic safety tire having an aspect ratio of 60% or more and, exhibiting a large deflection because of a large height, and use thereof under a large applied weight, maintaining properties during ordinary use under an inflated condition at high levels, enabling decrease in the weight, and showing remarkably improved properties under the run-flat condition in comparison with those of conventional safety tires having a rubber reinforcing layer.
As the result of extensive studies conducted by the present inventors to solve the above problems, particularly on the relation between the side wall portion of a tire and the properties during use under the run-flat condition, it was found that the above objects can be achieved by a layer of a fiber reinforced component which is prepared by covering specific filament fibers with rubber to form an integrated layer (a rubber-filament fiber composite) and disposed at the side wall in a vicinity of a carcass layer and other means as described in the following. The present invention has been completed based on the above knowledge.
An embodiment of the pneumatic safety tire of the present invention relates to a low profile safety tire which has an aspect ratio less than 60% and shows a small deflection because it has a small height and is used under a small applied load (referred to as an embodiment of the low profile tire).
Another embodiment of the pneumatic safety tire of the present invention relates to a general use safety tire for passenger cars which has an aspect ratio of 60% or more and shows a large deflection because it has a large height and is used under a large applied load (referred to as an embodiment of the general use tire).
With respect to both embodiment of the low profile tire and embodiment of the general use tire, (1) the pneumatic safety tire comprises:
a pair of left and right bead ring-shaped cores;
a carcass layer formed from layers in which a plurality of cords disposed parallel to each other are embedded in a covering rubber, both end portions of said carcass layer being folded over said bead cores and turned up such that said carcass layer is formed in an annular shape;
a multi-layer belt portion disposed at an outer side of said carcass portion in a radial direction of the tire;
an annular tread portion disposed at an outer side of said belt portion in the radial direction of the tire;
a pair of side wall portions disposed at the left and right of said tread portion;
wherein at least one sheet of a rubber-filament fiber composite formed from filament fibers and a rubber component is disposed at said side wall portions in a vicinity of said carcass layer.
With respect to the embodiment of the low profile tire, the present invention also provides:
(2) A pneumatic safety tire described in (1), wherein an aspect ratio of said tire is less than 60%, and at least one sheet of said rubber-filament fiber composite is disposed at said side wall portions in a vicinity of said carcass layer;
(3) A pneumatic safety tire described in (2), wherein said rubber-filament fiber composite is disposed at an inner side of said carcass layer;
(4) A pneumatic safety tire described in (2), wherein said rubber-filament fiber composite is disposed both at an inner side of said carcass layer and between said side wall portions and an outer surface of said carcass layer;
(5) A pneumatic safety tire described in (2), wherein said rubber-filament fiber composite is disposed between said side wall portions and an outer surface of said carcass layer, and a rubber reinforcing layer having a crescent-shaped cross-section is disposed at an inner side of said carcass layer;
(6) A pneumatic safety tire described in (2), wherein said rubber-filament fiber composite is disposed at an inner surface of a rubber reinforcing layer having a crescent-shaped cross-section which is disposed at an inner side of said carcass layer;
(7) A pneumatic safety tire described in (2), wherein 4 to 50% by weight of said rubber-filament fiber composite is the filament fibers; and
(8) A pneumatic safety tire described in (2), wherein said rubber-filament fiber composite is formed from a rubber and a non-woven fabric having a weight per area of 10 to 300 g/m2.
With respect to the embodiment of the general use tire, the present invention provides:
(9) A pneumatic safety tire described in (1), wherein an aspect ratio of said tire is 60% or more, and at least one sheet of said rubber-filament fiber composite is disposed at said side wall portions in a vicinity of said carcass layer;
(10) A pneumatic safety tire described in (9), wherein an aspect ratio of said tire is 60% or more, a rubber reinforcing layer having a crescent-shaped cross-section is disposed at an inner side of said carcass layer, and at least one sheet of said rubber-filament fiber composite is disposed at an inner side of said rubber reinforcing layer which is disposed at the inside of said carcass layer;
(11) A pneumatic safety tire described in (10), wherein at least one down carcass layer is additionally disposed between said side wall portions and an outer surface of said carcass layer;
(12) A pneumatic safety tire described in (10), wherein in addition to being disposed at the inner side of said rubber reinforcing layer, said rubber-filament fiber composite is also disposed between said side wall portions and an outer surface of said carcass layer;
(13) A pneumatic safety tire described in (12), wherein at least one down carcass layer is disposed between the outer surface of said carcass layer and said rubber-filament fiber composite which is disposed at the outer side of said carcass layer in the radial direction of said tire;
(14) A pneumatic safety tire described in (9), wherein an aspect ratio of said tire is 60% or more, a rubber reinforcing layer having a crescent-shaped cross-section is disposed at an inner side of said carcass layer, and at least one sheet of said rubber-filament fiber composite is disposed between said side wall portions and an outer surface of said carcass layer;
(15) A pneumatic safety tire described in (14), wherein at least one down carcass layer is additionally disposed between the outer surface of said carcass layer and said rubber-filament fiber composite which is disposed at the outer side of said carcass layer in the radial direction of said tire;
(16) A pneumatic safety tire described in (9), wherein 4 to 50% by weight of said rubber-filament fiber composite is the filament fibers, and the filament fibers are fibers which do not exhibit meltability when the tire is used under a run-flat condition;
(17) A pneumatic safety tire described in (9), wherein said rubber-filament fiber composite is formed from a rubber and a non-woven fabric having a weight per area of 10 to 300 g/m2, and the filament fibers do not exhibit meltability when the tire is used under a run-flat condition;
(18) A pneumatic safety tire described in (9), wherein the filament fibers in said rubber-filament fiber composite do not exhibit meltability at 270xc2x0 C. or lower;
(19) A pneumatic safety tire described in (18), wherein the filament fibers are at least one type of fibers selected from the group consisting of polyester fibers, aramide fibers, polyimide fibers, carbon fibers, glass fibers, and steel fibers; and
(20) A pneumatic safety tire described in (1), wherein said rubber-filament fiber composite is formed from a rubber component and filaments having a diameter or a maximum cross-sectional dimension of 0.0001 to 0.1 mm and a length of 8 mm or more, and said rubber filament fiber composite has a thickness of 0.05 to 2.0 mm.